Complexity is a term generally used to indicate a quality where many aspects or parts of specific entities or systems interact or form patterns with each other in varying ways. Observing and assessing these patterns of relationships are the focus of diverse scientific and mathematical studies of complex systems.

Stephen Hawking:I think the next [21st] century will be the century of complexity. We have already discovered the basic laws] that govern matter and understand all the normal situations. We don’t know how the laws fit together, and what happens under extreme conditions. But I expect we will find a complete unified theory sometime this century. There is no limit to the complexity that we can build using those basic laws.

The recognition of the importance of complex systems in physics and biology has led to their study in economic systems, usually characterized as governed by a large set of interacting nonlinear dynamic systems. It is clear that these phenomena are observable and are not necessarily inconsistent with standard economic reasoning. Professor Rosser has collected a large number of papers, some from not-easily-accessible sources, which show the application of complex system theory to a variety of economic phenomena. This collection will be invaluable to the development of new and necessary thinking in economics.

Complexity theory is really a movement of the sciences. Standard sciences tend to see the world as mechanistic. That sort of science puts things under a finer and finer microscope. In biology the investigations go from classifying organisms to functions of organisms, then organs themselves, then cells, and then organelles, right down to protein and enzymes, metabolic pathways, and DNA. This is finer and finer reductionist thinking.The movement that started complexity looks in the other direction. It’s asking, how do things assemble themselves? How do patterns emerge from these interacting elements? Complexity is looking at interacting elements and asking how they form patterns and how the patterns unfold. It’s important to point out that the patterns may never be finished. They’re open-ended. In standard science this hit some things that most scientists have a negative reaction to. Science doesn’t like perpetual novelty.

Let us keep the discoveries and indisputable measurements of physics. But … A more complete study of the movements of the world will oblige us, little by little, to turn it upside down; in other words, to discover that if things hold and hold together, it is only by reason of complexity, from above.

I actually enjoy complexity that's empowering. If it challenges me, the complexity is very pleasant. But sometimes I must deal with complexity that's disempowering. The effort I invest to understand that complexity is tedious work. It doesn't add anything to my abilities.

The complexity that we despise is the complexity that leads to difficulty. It isn't the complexity that raises problems. There is a lot of complexity in the world. The world is complex. That complexity is beautiful. I love trying to understand how things work. But that's because there's something to be learned from mastering that complexity.

Ward Cunningham, in "The Simplest Thing that Could Possibly Work : A Conversation with Ward Cunningham" Part V (19 January 2004)

The theory of evolution by cumulative natural selection is the only theory we know of that is in principle capable of explaining the existence of organized complexity.

Cyberspace. A consensual hallucination experienced daily by billions of legitimate operators, in every nation, by children being taughtmathematical concepts… A graphic representation of data abstracted from banks of every computer in the humansystem. Unthinkable complexity. Lines of light ranged in the nonspace of the mind, clusters and constellations of data. Like city lights, receding…

The most common human act that writing a novel resembles is lying. The working novelist lies daily, very complexly, and at great length. If not for our excessive vanity and our over-active imaginations, novelists might be unusually difficult to deceive.

We are glorious accidents of an unpredictable process with no drive to complexity, not the expected results of evolutionaryprinciples that yearn to produce a creature capable of understanding the mode of its own necessary construction.

I think the next [21st] century will be the century of complexity. We have already discovered the basic laws] that govern matter and understand all the normal situations. We don’t know how the laws fit together, and what happens under extreme conditions. But I expect we will find a complete unified theory sometime this century. There is no limit to the complexity that we can build using those basic laws.

As with real reading, the ability to comprehend subtlety and complexity comes only with time and a lot of experience. If you don't adequately acquire those skills, moving out into the real world of real people can actually become quite scary.

No matter what field a leader is in, he will face problems. They are inevitable for three reasons; first, we live in a world of growing complexity and diversity; second, we interact with people; and third, we cannot control all the situation we face.

Complexity has the propensity to overload systems, making the relevance of a particular piece of information not statistically significant. And when an array of mind-numbing factors is added into the equation, theory and models rarely conform to reality.

The inherent nature of complexity is to doubt certainty and any pretense to finite and flawless data. Put another way, under uncertainty principles, any attempt by political systems to ‘impose order’ has an equal chance to instead ‘impose disorder.’